Containers and methods for protecting pressure vessels

ABSTRACT

A container includes one or more hollow shell assemblies, each assembly having a first hollow shell including a first inner surface to cover a portion of a pressure vessel (PV) and a second hollow shell including a second inner surface attachable to the first hollow shell. The first and/or second hollow shells may include a fiber layer that may be at least partially impregnated with resin, and an energy dissipating material that is substantially concentric with the inner surfaces of the respective shells. The first and second hollow shells are attachable to one another to define a volume for at least partially enclosing the PV, and may be overwrapped via filament winding.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 17/340,568, filed on Jun. 7, 2021, which claims thebenefit of U.S. Provisional Patent Application No. 63/195,295, filed onJun. 1, 2021, and entitled “Containers and Methods for ProtectingPressure Vessels,” the entire contents of each of which are incorporatedby reference herein.

FIELD

This application relates to pressure vessels.

BACKGROUND

Pressure vessels (PVs) are reservoirs configured to store fluids, suchas liquids or gases, under pressure. The pressure may be substantiallyhigher than ambient pressure, e.g., may exceed 200 bars. The fluidwithin the PV may be dangerous, either on its own or when underpressure. For example, some PVs may be used to store hydrogen at apressure of about 700 bars. While it may be desirable to use pressurizedhydrogen or other pressurized fuels as a fuel source, PVs that are usedin vehicles (such as cars, trucks, airplanes, spacecraft, and the like)may undergo sudden movements, such as may be caused by a crash or suddenstop. If the PV fails, the resulting leak or explosion may be dangerousor even catastrophic. Accordingly, improved methods of protecting PVsare needed.

SUMMARY

Containers and methods for protecting pressure vessels are providedherein.

In accordance with one aspect of the present disclosure, an apparatusfor protecting a pressure vessel is provided. The apparatus may includea first hollow shell having a first inner surface sized and shaped tocover a first portion of the pressure vessel, and a second hollow shellhaving a second inner surface and sized and shaped to be attached to thefirst hollow shell so as to define a volume for at least partiallyenclosing the pressure vessel. The first and second hollow shells may beattached to one another so as to overwrap the pressure vessel with aplurality of plies. At least a portion of the plurality of plies may behelicoidally arranged relative to one another. In some embodiments, thefirst and second hollow shells define a volume for fully enclosing thepressure vessel. The first and second inner surfaces may be at leastpartially cylindrical, at least partially spherical, or at leastpartially conical. Moreover, the plurality of plies may be helical pliesthat are helicoidally arranged relative to one another. For example, theplies may include interwoven tows.

The apparatus further may include a third hollow shell having a thirdinner surface sized and shaped to cover a second portion of the pressurevessel, and a fourth hollow shell having a fourth inner surface andsized and shaped to be attached to the third hollow shell so as todefine a volume for at least partially enclosing the pressure vessel.Accordingly, the first and second hollow shells may define a volume forat least partially enclosing the first portion of the pressure vessel,and the third and fourth hollow shells may define a volume for at leastpartially enclosing the second portion of the pressure vessel. Forexample, the first portion of the pressure vessel may be disposed on aside of the pressure vessel opposite to the second portion of thepressure vessel.

In some embodiments, the apparatus may include a third hollow shellhaving a third inner surface, and which is sized and shaped to beattached to the second hollow shell so as to define the volume for atleast partially enclosing the pressure vessel. Moreover, the apparatusmay include a fourth hollow shell having a fourth inner surface, andwhich is sized and shaped to be attached to the third hollow shell so asto define the volume for at least partially enclosing the pressurevessel.

The first hollow shell may include a first fiber layer that issubstantially concentric with the first inner surface and is at leastpartially impregnated with a resin. In addition, the first hollow shellfurther may include a first energy dissipating material that issubstantially concentric with the first inner surface and is disposedbetween the first inner surface and the first fiber layer. The firstfiber layer may include a dry reinforcement that may be impregnatedduring placement of the first hollow shell on the pressure vessel.Additionally, the second hollow shell may include a second fiber layerthat is substantially concentric with the second inner surface and is atleast partially impregnated with a resin. Moreover, the second hollowshell further may include a second energy dissipating material that issubstantially concentric with the second inner surface and is disposedbetween the second inner surface and the second fiber layer. Inaddition, the second fiber layer may include a dry reinforcement thatmay be impregnated during placement of the second hollow shell on thefirst hollow shell.

Moreover, at least one of the first or second hollow shells may includeat least one of glass, carbon, natural fiber, or aramid. In addition, atleast one of the first or second hollow shells may include athermoplastic. At least one of the first or second hollow shells may beformed via automated tape manufacturing. Additionally, the apparatusfurther may include an outer layer having a filament winding that may beattached to an outermost layer of the apparatus so as to define a volumefor enclosing the pressure vessel.

In accordance with another aspect of the present disclosure, a containerfor a pressure vessel is provided herein. The container may include afirst hollow shell including a first inner surface configured to receivea first portion of the pressure vessel. The container may include asecond hollow shell including a second inner surface configured toreceive a second portion of the pressure vessel. The first hollow shellmay include a first fiber layer that is substantially concentric withthe first inner surface and is at least partially impregnated with aresin. The first hollow shell may include a first energy dissipatingmaterial that is substantially concentric with the first inner surfaceand is disposed between the first inner surface and the first fiberlayer. The second hollow shell may include a second fiber layer that issubstantially concentric with the second inner surface and is at leastpartially impregnated with a resin. The second hollow shell may includea second energy dissipating material that is substantially concentricwith the second inner surface and is disposed between the second innersurface and the second fiber layer. The first and second hollow shellsmay be attachable to one another so as to define a volume for at leastpartially enclosing the pressure vessel.

In some examples, at least one of the first and second inner surfaces isat least partially cylindrical, at least partially spherical, at leastpartially conical.

Additionally, or alternatively, in some examples, at least one of thefirst and second inner surfaces is at least partially axisymmetric.

Additionally, or alternatively, in some examples, the first and secondhollow shells define a volume for substantially enclosing the pressurevessel.

Additionally, or alternatively, in some examples, the first hollow shelldefines a first half-cylinder, and the second hollow shell defines asecond half-cylinder.

Additionally, or alternatively, in some examples, the first hollow shelldefines a first bowl shape, and the second hollow shell defines a secondbowl shape.

Additionally, or alternatively, in some examples, at least one of thefirst and second fiber layers includes a plurality of helical plies.

In some examples, the helical plies may be helicoidally arrangedrelative to one another. Optionally, a first one of the helical plies(i=1) includes a plurality of tows that are wound next to each other atan angle of θ_(i=1) relative to an axis. Optionally, a second one of thehelical plies (i=2) includes a plurality of tows that are wound next toeach other at an angle of θ_(i=2) relative to an axis. Optionally,θ_(i=2) differs from θ_(i=1) by about 1 to about 25 degrees.

In some examples, the helical plies include interwoven tows. Optionally,a first one of the helical plies (i=1) includes tows that are interwovenat angles of (+α_(i=1)+θ_(i=1)) and (−α_(i=1)+θ_(i=1)) relative to anaxis. Optionally, a second one of the helical plies (i=2) includes towsthat are interwoven at angles of (+α_(i=2)+θ_(i=2)) and(−α_(i=2)+θ_(i=2)) relative to an axis. Optionally, θ₁₌₂ differs fromθ_(i=1) by about 1 to about 25 degrees.

Additionally, or alternatively, in some examples, the first energydissipating material defines the inner surface of the first hollowshell.

Additionally, or alternatively, in some examples, the first fiber layerdefines an outer surface of the first hollow shell.

Additionally, or alternatively, in some examples, the second energydissipating material defines the inner surface of the second hollowshell.

Additionally, or alternatively, in some examples, the second fiber layerdefines an outer surface of the second hollow shell.

Additionally, or alternatively, in some examples, the first hollow shellfurther includes a third fiber layer that is substantially concentricwith the first inner surface; and a third energy dissipating materialthat is substantially concentric with the first inner surface and isdisposed between the first fiber layer and the third fiber layer.

Additionally, or alternatively, in some examples, the second hollowshell further includes a fourth fiber layer that is substantiallyconcentric with the second inner surface; and a fourth energydissipating material that is substantially concentric with the secondinner surface and is disposed between the second fiber layer and thefourth fiber layer.

Additionally, or alternatively, in some examples, the first hollow shellincludes a first helicoidally braided layer or woven fabric that isdisposed between the first inner surface and the first fiber layer.

Additionally, or alternatively, in some examples, the second hollowshell includes a second helicoidally braided layer or woven fabric thatis disposed between the second inner surface and the second fiber layer.Optionally, the resin of the first fiber layer at least partiallyimpregnates the first helicoidally braided layer or woven fabric, or theresin of the second fiber layer at least partially impregnates thesecond helicoidally braided layer or woven fabric.

Additionally, or alternatively, in some examples, fibers of the firstfiber layer and the second fiber layer independently include at leastone material selected from the group consisting of: ultra-high molecularweight polyethylene (UHMWPE), para-aramid, carbon, graphite, glass,aramid, basalt, ultra-high molecular weight polypropylene (UHMWPP), anatural material, a metal, quartz, ceramic, and recycled fiber.

Additionally, or alternatively, in some examples, at least one of thefirst and second energy dissipating materials includes a foam.Optionally, the foam includes polyvinylchloride (PVC), expandablepolyurethane (PU), expanded polystyrene (EPS), expanded polypropylene(EPP), polyethylene (PE), aluminum foam, radially oriented scaffolding3D printed material, honeycomb structure, closed cell foam, open cellfoam, viscoelastic gel, or defines a metamaterial.

Additionally, or alternatively, in some examples, the first fiber layerincludes substantially the same composition as the second fiber layer.

Additionally, or alternatively, in some examples, the first fiber layerincludes a different composition than the second fiber layer.

Additionally, or alternatively, in some examples, the first fiber layerincludes substantially the same material configuration as the secondfiber layer.

Additionally, or alternatively, in some examples, the first fiber layerincludes a different material configuration than the second fiber layer.

Additionally, or alternatively, in some examples, the first energydissipating material includes substantially the same composition as thesecond energy dissipating material.

Additionally, or alternatively, in some examples, the first energydissipating material includes a different composition than the secondenergy dissipating material.

Additionally, or alternatively, in some examples, the first energydissipating material includes substantially the same materialconfiguration as the second energy dissipating material.

Additionally, or alternatively, in some examples, the first energydissipating material includes a different material configuration thanthe second energy dissipating material.

Additionally, or alternatively, in some examples, the container furtherincludes a first fastener attached to the first hollow shell; and asecond fastener attached to the second hollow shell and configured toengage with the first fastener to attach the first hollow shell to thesecond hollow shell. Optionally, the first fastener includes a firstthread and the second fastener includes a second thread configured torotatably engage with the first thread. Optionally, the first fastenerincludes a toggle latch, pipe clamp, or bolted joint.

Additionally, or alternatively, any of the containers provided hereinmay include a sensor embedded within or between one or more layers ofthe container. Optionally, the sensor includes a piezoelectric sensorconfigured to monitor impact. Optionally, the sensor includes a fiberBragg grating (FBG) configured to monitor for gas leaks.

Under another aspect, a method of protecting a pressure vessel isprovided herein. The pressure vessel may have first and second portions.The method may include inserting the first portion of the pressurevessel into the first hollow shell of any of the containers providedherein. The method may include inserting the second portion of thepressure vessel into the second hollow shell of the container of any ofthe containers provided herein. The method may include attaching thefirst hollow shell to the second hollow shell.

Under another aspect, another method of protecting a pressure vessel isprovided herein. The method may include overwrapping the pressure vesselwith a plurality of helical plies. The helical plies may be helicoidallyarranged relative to one another.

In some examples, a first one of the helical plies (i=1) includes aplurality of tows that are wound next to each other at an angle ofθ_(i=1) relative to an axis. Optionally, a second one of the helicalplies (i=2) includes a plurality of tows that are wound next to eachother at an angle of θ₁₌₂ relative to an axis. Optionally, θ_(i=2)differs from θ_(i=1) by about 1 to about 25 degrees.

In some examples, the helical plies include interwoven tows. Optionally,a first one of the helical plies (i=1) includes tows that are interwovenat angles of (+α_(i=1)+θ_(i=1)) and (−α_(i=1)+θ_(i=1)) relative to anaxis. Optionally, a second one of the helical plies (i=2) includes towsthat are interwoven at angles of (+α_(i=2)+θ_(i=2)) and(−α_(i=2)+θ_(i=2)) relative to an axis. Optionally, θ_(i=2) differs fromθ_(i=1) by about 1 to about 25 degrees.

Under still another aspect provided herein, a method of making acontainer for a pressure vessel is provided. The method may includeforming a first hollow shell, and forming a second hollow shell. Thefirst hollow shell may be formed using steps including shaping a firstenergy dissipating material to form a first inner surface configured toreceive a first portion of the pressure vessel; and forming a firstfiber layer, at least partially impregnated with a resin, over the firstenergy dissipating material so as to be substantially concentric withthe first energy dissipating material. The second hollow shell may beformed using steps including shaping a second energy dissipatingmaterial to form a second inner surface configured to receive a secondportion of the pressure vessel; and forming a second fiber layer, atleast partially impregnated with a resin, over the second energydissipating material so as to be substantially concentric with thesecond energy dissipating material. The first hollow shell beingattachable to the second hollow shell so as to at least partiallyenclose the pressure vessel.

Under yet another aspect provided herein, a pressure vessel is provided.The pressure vessel may include a plurality of helical plies. Thehelical plies may be helicoidally arranged relative to one another.

In some examples, a first one of the helical plies (i=1) includes aplurality of tows that are wound next to each other at an angle ofθ_(i=1) relative to an axis. Optionally, a second one of the helicalplies (i=2) includes a plurality of tows that are wound next to eachother at an angle of θ_(i=2) relative to an axis. Optionally, θ_(i=2)differs from θ_(i=1) by about 1 to about 25 degrees.

In some examples, the helical plies include interwoven tows. Optionally,a first one of the helical plies (i=1) includes tows that are interwovenat angles of (+α_(i=1)+θ_(i=2)) and (−α_(i=1)+θ_(i=1)) relative to anaxis. Optionally, a second one of the helical plies (i=2) includes towsthat are interwoven at angles of (+α_(i=2)+θ_(i=2)) and(−α_(i=2)+θ_(i=2)) relative to an axis. Optionally, θ_(i=2) differs fromθ_(i=1) by about 1 to about 25 degrees.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1B schematically illustrate cross-sectional views of an examplecontainer for a pressure vessel (PV).

FIGS. 2A-2B schematically illustrate cross-sectional views of assemblyof example containers about a PV.

FIGS. 3A-3C schematically illustrate example configurations of differentplies.

FIGS. 4A-4B schematically illustrate cross-sectional views of anotherexample container for a PV.

FIG. 5 schematically illustrates a cross-sectional view of anotherexample container for a PV.

FIG. 6 schematically illustrates a cross-sectional view of anotherexample container for a PV.

FIG. 7 schematically illustrates an example overwrapping for a PV.

FIG. 8 schematically illustrates an example construction for a PV.

FIGS. 9-12 illustrate example flows of operations in respective methodsfor making a container for a PV.

FIG. 13 illustrates an example flow of operations in a method forpreparing a PV.

FIG. 14A schematically illustrates a model of crack propagation throughan example helicoidal layup.

FIG. 14B is a plot of the energy release rate as a function of depth fordifferent pitch angles in the model of FIG. 14A.

FIGS. 15A and 15B schematically illustrate various views of anotherexample container for a PV.

FIG. 15C schematically illustrates a cross-sectional view of thecontainer of FIG. 15B.

FIG. 16 illustrates an example flow of operations for making thecontainer of FIGS. 15A-15C for a PV.

FIG. 17 illustrates an exemplary patch of the container of FIGS. 15A-15Chaving quadriaxial layers.

FIG. 18 illustrates formation of a patch via automated tapemanufacturing.

FIG. 19 illustrates exemplary steps for filament winding the containerof FIGS. 15A-15C.

FIG. 20 illustrates the containers of FIGS. 15A-15C having a filamentwinding without a helicoidal layup.

DETAILED DESCRIPTION

Containers and methods for protecting pressure vessels are providedherein.

As provided herein, PVs (such as hydrogen pressure vessels, HPVs) may beprotected by partially or fully enclosing them within an impactresistant container, which may be referred to as a protective box or acrash box. The use of such a separate container may dissociate thepressure resistance function of the PV from the crash/impact resistanceof the container. For example, such a container, may inhibit damage tothe PV from impacts, such as from a crash or an external projectile.Because the container is separate from and encloses the PV, thestructural designs of the container and the PV may be individuallyoptimized, e.g., with different choices of fiber type, resin, andmanufacturing process. In some examples herein, the container may bedesigned as a laminate structure including at least one external fibercomposite shell (e.g., helicoidal composite shell) and at least oneenergy dissipating material, which may be referred to as a “core”. Thecontainer may be formed in two or more parts so as to accommodate theinsertion of the PV, and the parts may be attachable to one another soas to partially or fully enclose the PV therein, thus protecting it. Assuch, if the container becomes damaged, it may be readily replaced withanother such container without the need to replace the PV, which may becumbersome, expensive, and dangerous. In some examples herein, a damagedcontainer may be repaired and then reused with the same or a differentPV. In other examples herein, the PV itself may be overwrapped with aplurality of helical plies that are arranged helicoidally relative toone another, or the PV even may be formed using a plurality of helicalplies that are arranged helicoidally relative to one another.

FIGS. 1A-1B schematically illustrate cross-sectional views of an examplecontainer 110 for a PV 100. Container 110 at least partially encloses PV100, and in some examples substantially encloses or even fully enclosesPV 100. As used herein, to “at least partially enclose” a PV is intendedto mean that at least a portion of the PV is surrounded by a container.To “substantially enclose” a PV is intended to mean that a majority ofthe PV (e.g., more than 50%, more than 60%, more than 70%, more than80%, more than 90%, more than 95%, more than 98%, or up to 99% of thePV) is surrounded by the container, while the balance of the PV (e.g.,1% or more) is not surrounded by the container. In the illustratedexample, a neck portion 101 of PV 100 may protrude from container 110such that the fluid within the PV may be used, while the balance of thePV may be enclosed within container 110. In this example, PV 100 may beconsidered to be substantially enclosed within container 110, becausethe main reservoir of PV 100 is completely enclosed within container110, while another portion of PV 100 (here, the neck 101, or even only aportion of the neck) protrudes from the container. To “fully enclose” aPV is intended to mean that the entirety of the PV is surrounded by thecontainer.

Container 110 may include a first hollow shell 120 and a second hollowshell 130. First hollow shell 120 may include a first inner surface 121configured to receive a first portion of the pressure vessel 100. Firsthollow shell 120 may include a first fiber layer 122 that issubstantially concentric with the first inner surface and is at leastpartially impregnated with a resin. First hollow shell 120 also mayinclude a first energy dissipating material 123 that is substantiallyconcentric with the first inner surface 121 and is disposed between thefirst inner surface 121 and the first fiber layer 122. Second hollowshell 130 may include a second inner surface 131 configured to receive asecond portion of the pressure vessel 100. Second hollow shell 130 mayinclude a second fiber layer 132 that is substantially concentric withthe second inner surface 131 and is at least partially impregnated witha resin. Second hollow shell 130 also may include a second energydissipating material 133 that is substantially concentric with thesecond inner surface and is disposed between the second inner surfaceand the second fiber layer. The first and second hollow shells 120, 130may be attachable to one another so as to define a volume for at leastpartially enclosing the pressure vessel 100. In the nonlimiting exampleillustrated in FIG. 1A, first and second hollow shells 120, 130 meet oneanother at junction 140. Example structures for attaching hollow shellsto one another are described with reference to FIGS. 2A-2B. It should beappreciated that use of labels such as “first,” “second,” and the liketo refer to elements is not intended to imply any particular spatialrelationship between those elements.

In the nonlimiting example illustrated in FIGS. 1A-1B, the first energydissipating material 123 may define the inner surface 121 of the firsthollow shell 120, and the first fiber layer 122 may define an outersurface of the first hollow shell. Similarly, the second energydissipating material 133 may define the inner surface 131 of the secondhollow shell 130, and the second fiber layer 132 may define an outersurface of the second hollow shell. However, such layers may have anysuitable arrangement relative to one another and relative to the innerand outer surfaces of their respective hollow shells. Furthermore, theinner and outer surfaces may include any suitable combination of fiberlayer(s), energy dissipating material(s), and/or other layers. Someadditional, nonlimiting examples of alternative arrangements will bedescribed with reference to FIGS. 4A-4B, 5, 6, and 15A-15C. Exampleconfigurations of fiber layers, such as first fiber layer 122 aredescribed further below with reference to FIGS. 3A-3C.

It will be appreciated that container 110, and other containersdescribed elsewhere herein, may include any suitable combination ofshapes suitable to at least partially enclose PV 100. Illustratively,the inner surface 121 of hollow shell 120 may be shaped so as to followthe form of, and contact, the respective portion of the outer surface ofPV 100. Similarly, the inner surface 131 of hollow shell 130 may beshaped so as to follow the form of, and contact, the respective portionof the outer surface of PV 100. As such, different portions of thehollow shells 120, 130 may be shaped differently than one another, andmay have any suitable cross-section. Illustratively, at least one of thefirst and second inner surfaces 121, 131 is at least partiallycylindrical, at least partially spherical, or at least partiallyconical. In the nonlimiting example illustrated in FIG. 1A-1B, a portionof first inner surface 121 is cylindrical, while another portion offirst inner surface 121 is spherical, and inner surface 131 isspherical. As such, the first hollow shell 120 may be considered todefine a first bowl shape, and the second hollow shell 130 may beconsidered to define a second bowl shape. Other shapes readily may beenvisioned so as to partially, substantially, or fully enclose PVs foruse in any suitable context, such as in vehicles (cars, trucks,airplanes, spacecraft, and the like). In this regard, use of the term“substantially concentric” to describe the spatial relationship betweentwo materials is intended to refer to those materials having shapes withsubstantially the same center as one another, rather than to imply thatthe materials necessarily have a particular shape of cross-section(e.g., cylindrical, conical, or spherical).

For example, FIGS. 2A-2B schematically illustrate cross-sectional viewsof assembly of example containers about a PV. In the nonlimiting exampleillustrated in FIG. 2A, container 210 includes a first hollow shell 220that defines a first half-cylinder, and a second hollow shell 230 thatdefines a second half-cylinder. In the nonlimiting example illustratedin FIG. 2A, first and second hollow shells 220, 230 meet one another atjunction 240. As such, the composite cross-section of container 210 maybe substantially cylindrical in the region shown in FIG. 2A. Container210 may be shaped differently in other regions (not specifically shown),if present.

Any suitable structure may be used to attach the first and second hollowshells to one another, e.g., to attach first and second hollow shells120, 130 to one another, or to attach first and second hollow shells220, 230 to one another. Illustratively, container 110 or 210 (or anyother container provided herein) may include a first fastener attachedto the first hollow shell; and a second fastener attached to the secondhollow shell and configured to engage with the first fastener to attachthe first hollow shell to the second hollow shell. For example, incontainer 210 illustrated in FIG. 2A, the first and second fasteners(collectively designated 250) may include respective portions of atoggle latch, pipe clamp, or bolted joint. Optionally, container 210also may include padding 260 located about junction 240. As anotherexample, container 211 illustrated in FIG. 2B may be configuredsimilarly as container 110 illustrated in FIGS. 1A-1B, e.g., may includefirst hollow shell 221 configured similarly as first hollow shell 120,and may include second hollow shell 231 configured similarly as secondhollow shell 130. PV 100 may be partially, substantially, or fullyenclosed within container 211 by inserting the PV into first hollowshell 221, covering the PV's exposed end with second hollow shell 231,and securing the first and second hollow shells to one another usingfirst and second fasteners. In container 211, the first and secondfasteners (collectively designated 251) may include respective portionsof a toggle latch, pipe clamp, or bolted joint, and may include padding261. Alternatively, the first fastener may include a first thread andthe second fastener may include second thread configured to rotatablyengage with the first thread. That is, the first and second fasteners ofcontainer 211 may be configured such that second hollow shell 231 may bescrewed onto first hollow shell 221 so as to define an internal volumethat accommodates PV 100.

The first fiber layer of the first hollow shell (e.g., hollow shell 120,220, or 221) may include one or more plies, each of which may have anysuitable configuration. Similarly, the second fiber layer of the secondhollow shell (e.g., hollow shell 130, 230, or 231) may include one ormore plies, each of which may have any suitable configuration. Thecomposition and material structure of the first fiber layer of the firsthollow shell may be similar to, or may be different than, that of thesecond fiber layer of the second hollow shell. In some examples, thefirst fiber layer, the second fiber layer, or both the first and secondfiber layers, may include a woven fabric, a braided layer, or one ormore helical plies. As used herein, the term “woven fabric” is intendedto mean an element formed by interlacing two or more tows at rightangles to one another. As used herein, the term “tow” is intended tomean a flexible member that is elongated along a longitudinal axis ofthe tow, such as a thread, rope, filament, or tape. A tow may bemonolithic or may include a plurality of fibers. In some examples, a towmay include a plurality of fibers that are at least partiallyimpregnated with a resin and elongated along a longitudinal axis of thetow. As used herein, the term “braided layer” is intended to mean anelement formed by interlacing three or more tows together at non-rightangles to one another. As used herein, the term “helical,” whenreferring to a ply, is intended to mean that the tows of the ply arearranged in a spiral within that ply. As used herein, the term “ply” isintended to mean a layer that is distinguishable, whether by compositionor by material configuration, or both, from another layer. A ply mayinclude one layer, or may include multiple layers.

FIGS. 3A-3C schematically illustrate example configurations of differentplies. In the nonlimiting example illustrated in FIG. 3A, plies 321,322, 323 are located at a spaced distance from PV 100 (e.g., may beseparated from PV 100 by an energy dissipating material or may be placedone next to each other to form a fiber layer). In the illustratedexample, ply 321 may be the innermost most ply (“Ply 1”) of the firstfiber layer, ply 322 may be outside of ply 321 (“Ply 2”), and ply 323may be the outermost ply (“Ply 3”) of the first fiber layer, although itwill be appreciated that the first fiber layer may include any suitablenumber of plies. Plies 321, 322, 323 each may be helical. As illustratedin FIG. 3A, the tows in each ply may be wound next to one another toform a single ply with a distinct ply orientation. For example, the towsof ply 321 (i=1) may be wound next to each other at an angle of θ_(i=1)relative to axis 320 of PV 100 (which axis may be coaxial with the innersurface 340 of the first hollow shell); the tows of ply 322 (i=2) may bewound next to each other at an angle of θ_(i=2) relative to axis 320;and the tows of ply 323 (i=3) may be wound next to each other at anangle of θ_(i=3) relative to the axis 320. Angles θ_(i=1), θ_(i=2), andθ_(i=3) indicate the fiber orientation of the tow with respect to aglobal reference axis (here, PV longitudinal axis 320). The differencesbetween the tow orientation of adjacent plies, i.e. θ_(i=2)−θ_(i=1), maybe referred to as pitch angles. When the difference between the anglesof adjacent plies θ_(i=2)−θ_(i=1), θ_(i=3)−θ_(i=2), θ_(i=4)−θ_(i=3) aresubstantially the same as one another, the resulting plies may bereferred to as having a constant pitch angle, and when such differencesbetween adjacent ply orientations are different than one another, theresulting plies may be referred to as not having a constant pitch angle.For example, θ_(i=2) may differ from θ_(i=1) by about 1 to about 25degrees, and θ_(i=3) may differ from θ_(i=2) by about 1 to about 25degrees. As a result of such differences between angles θ_(i=1),θ_(i=2), and θ_(i=3), helical plies 321, 322, 323 may be helicoidallyarranged relative to one another. Such a helicoidal arrangement mayconfer additional crash resistance to the container, and thus to PV 100.As used herein, a “helicoidal arrangement” or “helicoidal layup,” whenreferring to a plurality of plies, is intended to mean that the tows ofadjacent plies are arranged at different angles than one another todefine a spiral. So, each of plies 321, 322, 323 may be helical, and thearrangement of plies 321, 322, 323 also may be helicoidal. As usedherein, by “about” and “substantially” it is meant within ±10% of thestated value. Plies helicoidally arranged allow for a smooth inter-ply(pitch) angle transitions between adjacent plies. This results in asmooth transition in elastic properties, which reduce interlaminar shearstresses at the interface between plies. These stresses are responsiblefor the formation of delamination under impact event. Therefore, thehelicoidal layup helps to delay, reduce, or inhibit the occurrence ofdamage. Additionally, the helicoidal layup is capable of dissipatingenergy, primarily via the formation of matrix damage. For example,cracks may grow and propagate along tortuous paths, following the localfiber orientation (spiraling cracks) and thus, leaving fibers mostlyundamaged, leading to high energy dissipation, delayed, reduced, orinhibited catastrophic failure, and increased structural integrity.Cracks are able to follow the local fiber orientation during propagationhence inhibiting or preventing the fibers (critical load carryingcomponent) from failing. This results in extensive damage diffusion at asub-critical level (i.e. prior to penetration or substantial loss ofstiffness), characterized by the formation of matrix splits andhelicoidal distributions of delaminations.

Fiber layers may include still other arrangements of plies and/or oftows within plies. For example, FIG. 3B illustrates an example in whichhelical plies include interwoven tows. In the nonlimiting exampleillustrated in FIG. 3B, plies 331, 332, 333 of a first fiber layer of afirst hollow member are located at a spaced distance from PV 100 (e.g.,may be separated from PV 100 by an energy dissipating material). In theillustrated example, ply 331 may be the innermost most ply (“Ply 1”) ofthe first fiber layer, ply 332 may be outside of ply 321 (“Ply 2”), andply 333 may be the outermost ply (“Ply 3”) of the first fiber layer,although it will be appreciated that the first fiber layer may includeany suitable number of plies. Plies 331, 332, 333 each may be helical.For example, as illustrated in FIG. 3B, the tows of ply 331 (i=1) may beinterwoven at angles of (+α_(i=1)+θ_(i=1)) and (−α_(i=1)+θ_(i=1))relative to axis 320 of PV 100 (which may be coaxial with inner surface340 of the first hollow shell); the tows of ply 332 (i=2) may beinterwoven at angles of (+α_(i=2)+θ_(i=2)) and (−α_(i=2)+θ_(i=2))relative to axis 320; and the tows of ply 333 (i=3) may be interwoven atangles of (+α_(i=3)+θ_(i=3)) and (−α_(i=3)+θ_(i=3)) relative to axis320. Angles θ_(i=1), θ_(i=2), and θ_(i=3) may be different than oneanother. For example, θ_(i=2) may differ from θ_(i=1) by about 1 toabout 25 degrees, and θ_(i=3) may differ from θ_(i=2) by about 1 toabout 25 degrees. Angles α_(i=1), α_(i=2) and α_(i=3) may be differentthan one another. For example, α_(i=2) may differ from α_(i=1) by about1 to about 90 degrees, and α_(i=3) may differ from α_(i=2) by about 1 toabout 90 degrees. As a result of such differences between anglesθ_(i=1), θ_(i=2), and θ_(i=3), helical plies 331, 332, 333 may behelicoidally arranged relative to one another. Such a helicoidalarrangement may confer additional crash resistance to the container, andthus to PV 100. In a layer without interwoven tows, the interfacebetween adjacent plies in the layer may be represented with a smoothsurface substantially equivalent in shape to the shell. In a layer withinterwoven tows, the interface between adjacent plies is uneven due tothe tows of adjacent plies crossing each other. During a crash or impactevent on the PV, one of the critical failures likely to occur in thefiber-reinforced layers is delamination damage, i.e. debonding betweenadjacent tows belonging to two adjacent plies. The presence of an uneveninterface may constrain the delamination to deflect from its originalplane. This mechanism may obstruct, reduce, or inhibit delaminationpropagation, hence leading to an increased impact resistance.

FIG. 3C schematically illustrates a cross-section of a fiber layer 343including a plurality of helical plies 301-307 that are helicoidallyarranged relative to one another so as to form a helicoidal lay-up. Eachof helical plies 301-307 includes helical tows 311 within a resin matrix312. In the illustrate example, the orientations of the tows 311 withinrespective plies 301-307 differ from one another (e.g., in a manner suchas described with reference to FIG. 3A or 3B). The shape of fiber layer343 is concentric with PV axis 320. The fiber layer 343 withincross-section illustrated in FIG. 3C may, for example, correspond to thefiber layer 122 within cross-section 180 of container 110 described withreference to FIGS. 1A-1B, the fiber layer within cross-section 280 ofcontainer 210 described with reference to FIG. 2A, the fiber layerwithin cross-section 281 of container 211 described with reference toFIG. 2B (projected into the volume illustrated in FIG. 3C), the fiberlayer 422 within cross-section 480 of container 410 described withreference to FIGS. 4A-4B, the fiber layer 422′ within cross-section 480′of container 410 described with reference to FIGS. 4A-4B, the fiberlayer within cross-section 580 of container 510 described with referenceto FIG. 5 (projected into the volume illustrated in FIG. 3C), fiberlayer 622 within cross-section 680 of the first hollow shell 620 of thecontainer described with reference to FIG. 6 , fiber layer 622′ withincross-section 680′ of the first hollow shell 620 of the containerdescribed with reference to FIG. 6 , fiber layer 622″ withincross-section 680″ of the first hollow shell 620 of the containerdescribed with reference to FIG. 6 , the fiber layer withincross-section 780 of overwrapping 700 described with reference to FIG. 7, or the fiber layer within cross-section 880 of PV 800 described withreference to FIG. 8 . Although seven helical plies 301-307 areillustrated in FIG. 3C, it will be appreciated that any of the fiberlayers provided herein may include any suitable number of plies, e.g.,may include about 1-20 plies, or about 2-15 plies, or about 3-10 plies,or about 4-8 plies. Optionally, each such ply may be helically wound,and as a further option the helically wound plies may be helicoidallyarranged so as to provide one or more of the benefits such as describedherein.

As noted further above with reference to FIGS. 1A-1B, the first hollowshell, the second hollow shell, or both the first and second hollowshells may include one or more additional layers. Illustratively, FIGS.4A-4B schematically illustrate cross-sectional views of another examplecontainer 410 for a PV 100. Container 410 at least partially encloses PV100, and in some examples substantially encloses or even fully enclosesPV 100. In a manner similar to that described with reference to FIGS.1A-1B, container 410 may include a first hollow shell 420 and a secondhollow shell 430. First hollow shell 420 may include a first innersurface 421 configured to receive a first portion of PV 100. Firsthollow shell 420 may include a first fiber layer 422 that issubstantially concentric with the first inner surface and is at leastpartially impregnated with a resin. First hollow shell 420 also mayinclude a first energy dissipating material 423 that is substantiallyconcentric with the first inner surface 421 and is disposed between thefirst inner surface 421 and the first fiber layer 422. In thenonlimiting example illustrated in FIGS. 4A-4B, first hollow shell 420further may include an additional fiber layer 422′ that is substantiallyconcentric with the first inner surface 421, and an additional energydissipating material 423 that is substantially concentric with the firstinner surface and is disposed between the first fiber layer 422 and theadditional fiber layer 423. The additional fiber layer 422′ may be atleast partially impregnated with a resin.

Second hollow shell 430 illustrated in FIGS. 4A-4B may include a secondinner surface 431 configured to receive a second portion of PV 100.Second hollow shell 430 may include a second fiber layer 432 that issubstantially concentric with the second inner surface 431 and is atleast partially impregnated with a resin. Second hollow shell 430 alsomay include a second energy dissipating material 433 that issubstantially concentric with the second inner surface and is disposedbetween the second inner surface and the second fiber layer. In thenonlimiting example illustrated in FIGS. 4A-4B, second hollow shell 420further may include an additional fiber layer 432′ that is substantiallyconcentric with the second inner surface 431; and an additional energydissipating material 433′ that is substantially concentric with thesecond inner surface and is disposed between the second fiber layer andthe additional fiber layer. The first and second hollow shells 420, 430may be attachable to one another so as to define a volume for at leastpartially enclosing PV 100. In the nonlimiting example illustrated inFIG. 4A, first and second hollow shells 420, 430 meet one another atjunction 440. Example structures for attaching hollow shells to oneanother are described with reference to FIGS. 2A-2B.

In the nonlimiting example illustrated in FIGS. 4A-4B, the first energydissipating material 423 may define the inner surface 421 of the firsthollow shell 420, and the second energy dissipating material 433 maydefine the inner surface 431 of the second hollow shell 430, in asimilar manner to that described with reference to FIGS. 1A-1B.Additionally, the additional fiber layer 422′ may define an outersurface of the first hollow shell 420, and the additional fiber layer432′ may define an outer surface of the second hollow shell 430. Theadditional fiber layer and additional energy dissipating materialprovided in each of the first and second hollow shells 420, 430 mayprovide multiple stages of impact resistance. So as to provide stillfurther impact resistance, one or both of additional fiber layers 422′,432′ may include multiple plies, e.g., helical plies which optionallymay be helicoidally arranged, in a manner such as illustrated in FIG.4B. Optionally, one or more sensors may be embedded within or betweenone or more layers of container 410. The sensor(s) may include, forexample, a piezoelectric sensor configured to monitor impact, a fiberBragg grating (FBG) configured to monitor for gas leaks, or the like.Such sensor(s) may be attached to an appropriate monitoring system,e.g., via a wired or wireless communication pathway. In one nonlimitingexample, a FBG sensor will record and monitor alteration in the localstrain filed. Such alterations are the results of the presence ofdamage. Therefore, by placing FGB sensors at various depth in the shell,it is possible to detect upon an impact event the depth of the damage inthe crash box. This can be used to judge the durability of the crashbox, the remaining protection potential and whether this requiresreplacement or repair. The FBG signal can be processed with onboard live(wired or wireless) monitoring and calibrated to trigger recording atthe occurrence of specific alteration in the monitored signal. Dependingon the type of signal alteration it is possible to distinguish differenttypes of damage. For instance, a change in the peak of the recordedsignal will suggest the passage of a delamination while a fulltruncation of the signal will indicate the formation of a translaminarcrack (severe damage) that breaks the optical fiber carrying the FBGsensor. The presence of piezoelectric sensor, for instance in the formof a polymer, can be used both as leak detection indicator as well asdamage indicator upon impact. The piezoelectric sensor would provideindication of local change in pressure. This can be originating form aleak from the PV as well as from impact loading generated pressurestates. The entity of the transmission signal can be appropriatelycalibrated to correlate with potential leakages and severity andlocation of impact-damage events.

Additionally, or alternatively, in a manner such as illustrated in FIG.4A, one or both of energy dissipating materials 423, 433 may be shapedso as to provide additional impact resistance. For example, in a mannersuch as illustrated in FIG. 4A, the first energy dissipating material423 may be thicker within the spherical/bowl-shaped region configured toaccept a first end of PV 100, and the second energy dissipating material433 may be thicker within the spherical/bowl-shaped region configured toaccept a second end of PV 100, thus providing additional cushioningagainst any impacts to those end regions. Alternatively, one or both ofenergy dissipating materials 423, 433 may have a substantially uniformthickness. Note that first energy dissipating materials 123, 133described with reference to FIGS. 1A-1B similarly may be shaped in amanner such as described with reference to FIG. 4A, or may have asubstantially uniform thickness.

Additional and/or differently shaped energy dissipating material(s) maybe included so as to further enhance impact resistance. For example,FIG. 5 schematically illustrates a cross-sectional view of anotherexample container 510 for a PV 100. Container 510 may be configuredsimilarly to other containers described herein (e.g., container 110,210, 211, 410, or 610, details not specifically illustrated), and maycontain additional material 550 for cushioning a corresponding end of PV100 against impact. Such additional material may, for example, behelpful if one end of PV 100 is particularly vulnerable to impact, e.g.,forms the leading edge of a fuel tank. This region of the PV is in factmore susceptible to low velocity impact damage, especially duringtransportation and handling of the PV.

Still other configurations may be envisioned. For example, FIG. 6schematically illustrates a cross-sectional view of another examplecontainer for a PV. While FIG. 6 illustrates a cross-section of firsthollow shell 620 of a container, it will be appreciated that the secondhollow shell of the container may be configured similarly, or may beconfigured differently. In the example shown in FIG. 6 , first hollowshell 620 includes a first helicoidally braided layer or woven fabric660, which may be located at any suitable location within the firsthollow shell. Illustratively, the first helicoidally braided layer orwoven fabric 660 may be disposed between the first inner surface 621 anda fiber layer 622. Additionally, or alternatively, a fiber layer 622″may define the inner surface of first hollow shell 620. Optionally, anenergy dissipating layer 623 may be disposed internally, e.g., betweenfirst helicoidally braided layer or woven fabric 660 and fiber layer622″. The first hollow shell 620 (as well as other hollow shellsprovided herein) may include any suitable number and arrangement oflayers, which together may inhibit damage to PV 100 resulting from acrash. Illustratively, hollow shell 620 may include additionalhelicoidally braided layer or woven fabric 660′ disposed outside offiber layer 622, additional energy dissipating layer 632′ disposedoutside of additional helicoidally braided layer or woven fabric 660′,and additional fiber layer 622′ disposed outside of additional energydissipating layer 632′ and defining an outer surface of the first hollowshell 620.

Braids produced using 2D or 3D techniques offer an interesting propertyof diameter variation associated with fiber angle variation. As fiberscan slip within a tubular braid, this allows to expand or reduce thediameter of such braid. This property can be advantageous to create astructure having a helicoidal architecture with several layerseffectively sleeved over one another so as to progressively expand thediameter of the structure and to slightly vary the fiber angle betweenand/or along layers to create a very small clocking angle variationbetween two adjacent braided layers. Such braided fiber reinforcingstructures can also be provided in the form of a flat braided tapeobtained from a tubular braid cut along a longitudinal direction andthen laid open flat. The fiber angular orientation also varies with thewidth of the tape. Such braided tape can also be used to stack differentlayers of the same tape with slightly different fiber angle to create astructure having a helicoidal architecture. This property can also befound in woven fabrics which are skewed to modify the initial 90° anglebetween warp and weft which can be tuned to create a series of warp/weftangles with small angular variations from one fabric layer to the nextone (such as a 5° clocking angle to align layers at 90°, 85°, 80°, 75°degrees, etc.) thus creating a structure having a helicoidalarchitecture.

In examples in which a fiber layer is disposed adjacent to ahelicoidally braided layer or woven fabric, e.g., in a manner such asdescribed with reference to FIG. 6 , the resin of the fiber layer may atleast partially impregnate the helicoidally braided layer or wovenfabric. For example, if filament winding is used, both pre-impregnatedtows as well as dry fiber tows may be used. This means that during thecuring of the container part, part of the excess of resin of thepre-impregnated tows may flow into the dry tows. Depending on the excessof resin of the pre-impregnated tows, a specific degree of partialimpregnation of the dry tows may be obtained. The full or partialimpregnation of the helicoidally braided layer or woven fabric mayenhance impact resistance and gas leak detection, e.g., using a sensorsuch as described elsewhere herein. Within a fiber reinforced layer, thealternation of plies with higher degree of fiber impregnation to plieswith a lower degree of fiber impregnation leads to a variation inelastic properties between adjacent plies. These energy dissipationmechanisms, which include crack deflection, crack arrest and crackdiffusion allow for a higher damage resistance and structural integrityof the fiber layer. The effectiveness of these mechanisms increases withthe difference in elastic properties. Additionally, the presence ofpartially impregnated plies within a fiber layer will increase theflexibility of the shell. This will allow absorbance of a larger amountof energy under elastic deformation during an impact event beforereaching the failure point.

It will be appreciated that in examples where a hollow shell includestwo or more layers of a similar type (e.g., two or more fiber layers,two or more energy dissipating materials, or two or more helicoidallybraided layer or woven fabrics), each layer of that type may have thesame composition as one another, or the same material configuration asone another, or both the same composition and the same materialconfiguration as one another. As used herein, the term “composition” isintended to refer to the material(s) that are included in an element. Asused herein, the term “material configuration” is intended to refer tothe physical arrangement of the materials that are included in anelement. For example, two elements that have the same composition as oneanother may be made of substantially the same materials as one another.Those materials may have the same material configuration as one another,or may have different material configurations than one another. Or, forexample, two elements that have different compositions than one anothermay have the same material configuration as one another, or may havedifferent material configurations than one another. Illustratively, agiven ply may include tows with different longitudinal orientations thanone another; such tows may be part of the same elongated member as oneanother.

In one nonlimiting example, an inner fiber layer may include a helicoidhaving angles Δθ and α selected so as to arrest microcracking. Suchinner fiber layer may help to protect the gas under pressure, whileouter fiber layer(s) may have a different material configuration thanthe inner fiber layer. For example, the outer fiber layer may include ahelicoid having angles Δθ and α selected so as to protect against biggerimpacts, like a crash. The ranges of Δθ and α for increasingmicro-cracking resistance may, for example, be between 30° and 90°.Additionally, to further enhance micro-cracking resistance, thin-plytows may be used. The ranges of Δθ and α for protecting against largerimpact should be between 1° and 25°. Additionally, any suitablecombination of thin plies, standard plies, and/or thick plies may beused to achieve good impact resistance, reduce material costs and lay-uptime. A smaller range of Δθ and α may allow for cracks to propagate viamainly braking matrix, following the local fiber orientation dictated bythe helicoidal layup. This allows for a large quantity of energy to bedissipated along tortuous cracking patterns that leave fibers mostlyundamaged, hence preserving the structural integrity of the shell undera severe impact event.

Such distinction in the ranges of Δθ and α follows an analytical modeldescribing the evolution of the energy release rate (energy required fora crack to propagate in a certain material) at the front of a spiralingmatrix crack growing in a helicoidally arranged lay-up. The equationsdescribing the analytical model can be found in Mencattelli et al.,“Realising bio-inspired impact damage-tolerant thin-ply CFRP Bouligandstructures via promoting diffused sub-critical helicoidal damage,”Composites Science and Technology, 182, 107684 (2019), the entirecontents of which are incorporated by reference herein. The modeldescribes the growth of twisting spiraling crack via the analysis of thelocal energy release rate (G) along the crack front, with the crackstarting form an initially flat condition. A global reference system anda local one along the crack front fully define the crack front as ittwists and kinks at any given time FIG. 14A schematically illustrates amodel of crack propagation through an example helicoidal layup. FIG. 14Bis a plot of the energy release rate as a function of depth fordifferent pitch angles in the model of FIG. 14A. More specifically, FIG.14A illustrates a spiraling crack that initiates within ply-(0) withfibers aligned along the x-axis corresponding to the 0° orientation andthe longitudinal axis of the PV and then propagates through additionalplies (1), (2), (3), and (4) in the z direction (perpendicular to thelongitudinal axis of the PV, and in the radial direction of the PV). Thesurface of the crack may be described by the shaded curve 1401illustrated in FIG. 14A. A closed-form solution to the problem can beobtained by assuming that: (i) the crack only breaks matrix, and thematrix is isotropic; (ii) the crack front remains straight; (iii) otherfailure mechanisms such as delaminations and fiber breaks do not occur;and (iv) the initially flat crack is opened in Mode I, i.e. the cracksurfaces are opened with a displacement mainly applied along x, i.e.perpendicular to the crack surface. This opening condition is wellrepresentative of a translaminar crack that propagates radially throughthe PV. Following these assumptions is possible to obtain the equationsfor the evolution of the energy release rate at the front of thespiraling crack fully defined in the space x-y-z of the PV.

FIG. 14B illustrates the energy release rate (G/G₀, a dimensionlessquantity) for pitch angles (Δθ) of 2.5° (curve 1411), 5° (curve 1412),10° (curve 1413), 20° (curve 1414), and 45° (curve 1415). For example,an helicoidal layer with Δθ=20° (curve 1414) was modeled to have pliesstacked with the following orientations θ_(i) with respect to thelongitudinal axis of the PV:[0°/20°/40°/60°/80°/100°/120°/140°/160°/180°/200°/ . . . /1440°]. Thehelicoidal layer with Δθ=5° (curve 1412) was modeled to have pliesstacked with the following orientations θ_(i) with respect to thelongitudinal axis of the PV:[0°/5°/10°/15°/20°/25°/30°/35°/40°/45°/50°/715°/720°]. The other layups(with other pitch angles) were modeled similarly. In this nonlimitingexample the plies are made of carbon/epoxy UD thin-plies with a fiberareal weight of 20 g/m². Higher energy release rate means thatmicro-cracking will be promoted, allowing for diffuse damage and highenergy dissipation. Lower energy release rate means a lower chance forthe formation of micro-cracking. FIG. 14B is normalized by the value ofthe energy release rate (G₀) required to grow a flat crack parallel tothe x-z plane illustrated in FIG. 14A. It may be seen in FIG. 14B thatas pitch angle increases from 2.5° (curve 1411), to 5° (curve 1412), to10° (curve 1413), to 20° (curve 1414), and to 45° (curve 1415), theenergy release rate decreases. Accordingly, from FIG. 14B, it may beunderstood that by reducing Δθ, the crack resistance (under dominantMode I opening, such as under impact) to growing spiraling cracksdecreases, facilitating the propagation of micro-cracking. This allowsfor larger amount of energy being dissipated while preserving theintegrity of the fibers, and hence of the crash box. Increasing Δθ, thecrack resistance (under dominant Mode I opening) to growing spiralingcracks increases, delaying, reducing, or inhibiting the formation ofmicrocracking and promoting the occurrence of catastrophic mechanisms offailure, such as delaminations and fiber breaks. Therefore, while largerΔθ allows for a better micro-cracking resistance to avoid leakage (innerlayer), smaller Δθ allows to better resist impact and dissipate moreenergy at the impact location (outer layer). The inner and outer fiberlayers also or alternatively may have different compositions so as toenhance their respective performance for the intended function. Forexample, the inner layer could be made by a tough material highlyresistance to micro-cracking such as thin-ply carbon fiber embedded intoughened epoxy resin, while the external layer could be made of a fiberreinforcement with higher ductility than carbon fiber, such as glassfiber and/or aramid fibers or a combination of multiple fiber types.

Composite laminates including stacks of thin ply (TP) fiber-reinforcedmaterials may exhibit better mechanical properties and improvedresistance to micro-cracking and delamination when compared to samethickness parts made using thicker plies. TP fiber reinforced materialsrequire higher applied loads to form micro-cracks in the matrix,longitudinally to the fibers (i.e. matrix splits). This increasedmicro-cracking resistance leads to improved delamination resistance. Forexample, commercially available aerospace unidirectional (UD)carbon/epoxy (C/E) pre-pregs are grade 190 (0.0073 in/ply) or grade 145(0.0056 in/ply). TPUD is typically grade 75 (0.003 in/ply) or thinner.The grade specifies the nominal areal weight of carbon fiber in UDpre-preg measured in g/m². TP laminates allow for reduced minimum gaugeand/or lighter weight equivalent performance structures. TP materialsmay include, for example, unidirectional (UD) tapes, non-crimp fabrics(NCF) or woven materials. Laminates may include ply stacks that arebalanced (having about the same number of plus and minus orientationplies) and that are symmetric (that is, each ply above the midplane ofthe lay-up may have an identical ply (about the same material,thickness, and orientation) at about equal distance below the midplane).

It will be appreciated that any suitable materials, or combinations ofmaterials, may be used in the present containers. For example, as notedabove, the present fiber layers may be at least partially impregnatedwith a resin, e.g., a thermoset or thermoplastic resin such as known inthe art. The resin optionally may be or include a fire retardant, so asto further reduce the risk of explosion in the event of an impact. Inone nonlimiting example, the resin in the outer composite shell may beequipped with flame retardant material to reduce potential for flamedamage in case of a leak resulting from damage to the PV.

The present fiber layers may include any suitable material orcombination of materials. For example, fiber layers provided herein,independently of one another, may include at least one material selectedfrom the group consisting of: ultra-high molecular weight polyethylene(UHMWPE), para-aramid, carbon, graphite, glass, aramid, basalt,ultra-high molecular weight polypropylene (UHMWPP), a natural material(e.g., hemp or flax), a metal, quartz, ceramic, and recycled fiber. Thefibers within the present fiber layers may be expected to act as a loadspreader and sharp impact stopper that may distribute the energy of animpact onto a wider surface of energy dissipating material, thusinhibiting damage to the PV.

In some examples, the present energy dissipating materials may include afoam. The foam may, for example, include polyvinylchloride (PVC),expandable polyurethane (PU), expanded polystyrene (EPS), expandedpolypropylene (EPP), polyethylene (PE), aluminum foam, radially orientedscaffolding 3D printed material, honeycomb structure, closed cell foam,open cell foam, viscoelastic gel, or may define a metamaterial.Honeycomb structures are commercially available, e.g., aluminumhoneycombs, or NOMEX® which is a flame-resistant meta-aramid materialthat is commercially available from DuPont de Nemours, Inc. (Wilmington,Delaware). As used herein the term “metamaterial” is intended to referto a cellular, hierarchical structure which has similar properties ondifferent length scales, such as used in football helmets.

It will be appreciated that the first and second hollow shells of any ofthe containers provided herein may be used in any suitable method forprotecting a PV. Such a method may, for example, include inserting afirst portion of the PV into the first hollow shell of any of thepresent containers; inserting a second portion of the PV into the secondhollow shell of that container; and attaching the first hollow shell tothe second hollow shell.

It will also be appreciated that the teachings herein may be used toprotect PVs without necessarily creating a crash box that is separablefrom the PV. Illustratively, a method of protecting a PV may includeoverwrapping the pressure vessel with a plurality of helical plies,wherein the helical plies are helicoidally arranged relative to oneanother. FIG. 7 schematically illustrates an example overwrapping 700for a PV 100 (internal plies of PV 100 shown). Overwrapping 700 mayinclude with a plurality of helical plies, wherein the helical plies arehelicoidally arranged relative to one another. Alternatively, the PVitself may be formed so as to include a plurality of helical plies,wherein the helical plies are helicoidally arranged relative to oneanother. FIG. 8 schematically illustrates an example construction for aPV. PV 800 may include a plurality of helical plies, wherein the helicalplies are helicoidally arranged relative to one another. In a mannersimilar to that described with reference to FIG. 3A, a first one of thehelical plies (i=1) of PV 800 or of overwrapping 700 may include aplurality of tows that are wound next to each other at an angle ofθ_(i=1). A second one of the helical plies (i=2) may include a pluralityof tows that are wound next to each other at an angle of θ_(i=2).Optionally, θ_(i=2) may differ from θ_(i=1) by about 1 to about 25degrees, such that the plies define a helicoidal arrangement.Alternatively, in a manner similar to that described with reference toFIG. 3B, the helical plies may include interwoven tows. For example, afirst one of the helical plies (i=1) may include tows that areinterwoven at angles of (+α+θ_(i=1)) and (−α+θ_(i=1)). A second one ofthe helical plies (i=2) includes tows that are interwoven at angles of(+α+θ_(i=2)) and (−α+θ_(i=2)). Optionally, θ_(i=2) may differ fromθ_(i=1) by about 1 to about 25 degrees. In one nonlimiting example, atleast part of PV 800 may be created using helical layers conventionallywound around a sacrificial mandrel to resist the pressure load, and asecond outer plurality of plies arranged helicoidally to resist impacts.

The present containers, overwrappings for PVs, and PVs may be made usingany suitable combination of operations. FIGS. 9-12 illustrate exampleflows of operations in respective methods for making a container for aPV. Referring now to FIG. 9 , method 900 may include forming a firsthollow shell (operation 910), and forming a second hollow shell, thefirst hollow shell being attachable to the second hollow shell so as toat least partially enclose the PV (operation 920). The first hollowshell may be formed using steps that include shaping a first energydissipating material to form a first inner surface configured to receivea first portion of the pressure vessel (operation 911); and forming afirst fiber layer, at least partially impregnated with a resin, over thefirst energy dissipating material so as to be substantially concentricwith the first energy dissipating material (operation 912). The secondhollow shell may be formed using steps that include shaping a secondenergy dissipating material to form a second inner surface configured toreceive a second portion of the pressure vessel (operation 921); andforming a second fiber layer, at least partially impregnated with aresin, over the second energy dissipating material so as to besubstantially concentric with the second energy dissipating material(operation 922). The operations of method 900 may be used to preparecontainers such as described with reference to FIG. 1A-1B, 2A-2B, 4A-4B,5 , or 6.

Illustratively, operations 911, 912, 921, and 922 may be performed usingany suitable combination of operations such as illustrated in FIGS.10-12 . Referring now to FIG. 10 , method 1000 may include forming anenergy dissipating material (core) to a shaped mandrel, e.g., moldingfoam to a shape or winding honeycomb/foam strips of a core to a mandrelshape (operation 1010). Method 1000 may include winding, onto the energydissipating material (e.g., foam), helical layers with a helicoidallayup with variable or constant pitch angle (operation 1020). The towsused to form the helical layers may be at least partially impregnatedwith a resin. Method 1000 may include curing the structure (operation1030). Method 1000 may include removing the mandrel (operation 1040).Method 1000 may include inserting a PV into the resulting container(crash box) (operation 1050). Container 110 described with reference toFIGS. 1A-1B is a nonlimiting example of a container that may be madeusing operations such as described with reference to FIG. 10 .

Referring now to FIG. 11 , method 1100 may include winding helicallayers with a helicoidal layup with variable or constant pitch angle ona sacrificial mandrel, to form inner and outer shells (operation 1110).Method 1100 may include curing the resulting structure(s) (operation1120). Method 1100 may include removing the mandrel (operation 1130).Method 1100 may include injecting an energy dissipating material, e.g.,expandable polyurethane (PU) foam, between the shells to create asandwich crash box (operation 1140). Method 1100 may include inserting aPV into the resulting container (crash box) (operation 1150). Theresulting container may include inner and outer surfaces defined byrespective fiber layers, having an energy dissipating material disposedtherebetween.

Referring now to FIG. 12 , method 1200 may include trimming an energydissipating material, e.g., foam core, to a mandrel shape (operation1210). Method 1200 may include winding helical layers in a helicoidallayup with variable or constant pitch angle (operation 1220). Method1200 may include braiding layers to form a helicoidal braided structureor using additional energy dissipating material, e.g., foam (operation1230). Method 1200 may include impregnating the structure with a flameretardant additive resin (operation 1240). Method 1200 may includewinding helical layers in a helicoidal layup (operation 1250).Operations 1230 through 1250 may be repeated any suitable number oftimes, e.g., one, two, three, or more than three times. Method 1200 mayinclude curing the structure (operation 1260). Method 1200 may includeremoving the mandrel (operation 1270). Method 1200 may include insertinga PV into the resulting container (crash box) (operation 1280). Thecontainer described with reference to FIG. 6 is a nonlimiting example ofa container that may be made using operations such as described withreference to FIG. 12 .

FIG. 13 illustrates an example flow of operations in a method 1300 forpreparing a PV. Method 1300 may include winding helical layers in ahelicoidal fashion (operation 1310). Method 1300 may include curing thestructure (operation 1320). Method 1300 may include removing the mandrel(operation 1330). The PV described with reference to FIG. 8 is anonlimiting example of a PV that may be made using operations such asdescribed with reference to FIG. 13 .

It will be appreciated that the use of a separated protective crash box(container), such as provided herein, may allow the weight andcomplexity of the PV to be reduced. Indeed, in previously knownfiber-reinforced composite PVs including, the fibers may constantly beunder a tensile stress due to the pressurized gas. With fiber-reinforcedcomposite materials, such tensional state may lead to a reduction of theimpact strength, e.g., in a manner such as described in Kamarudin etal., “Effect of high velocity ballistic impact on pretensioned carbonfibre reinforced plastic (CFRP) plates,” TOP Conference Series:Materials Science and Engineering 165(1): 012005 (2017), the entirecontents of which are incorporated by reference herein. The presentinventors have recognized that previously known composite PVs areoverbuilt to mitigate the tensile stress, for example, that overbuildingthe PVs may increase impact performance while also increasing structuralweight, hence leading to a non-efficient design. In comparison, becausethe separate protective containers provided herein need not bepressurized, the impact properties will not be degraded, and thematerial can be used more efficiently.

In some examples, such as described with reference to FIGS. 4A-4B and 6, the present containers may be constructed in a multi-core structurewith alternating helicoidal sub-laminates and energy dissipatingmaterial (e.g., foam) layers. Such an arrangement may create periodicchanges in elastic properties which are expected to function as a crackarrest mechanism for impact damage. This is expected to confer amultiple impact resistance to the container, which in turn is expectedto extend the operating life of the PV.

In other examples, the multi-core structure may include alternatinghelicoidal sub-laminates and partially impregnated dry fiber reinforcedlayers. The partial impregnation may be achieved using an overimpregnated filament wound helicoidal sub-laminates to bleed out theexcess of resin and partially impregnate the dry fiber layers. This maycreate a leak detection system at different stages in the crash box aswell as to improve impact performances. Additionally, or alternatively,a partially impregnated layer may provide a periodic change in elasticproperties that promote crack arrest and higher damage tolerance.

Additionally, or alternatively, the energy dissipating material (e.g.,foam core) may be equipped with piezoelectric/FBG sensing responsive topressure/strain. The most external layers may be used to detect impactdamage and its depth without the need of downtime to service the crashbox. This may provide for live monitoring of the safety margin change ofthe crash box. The innermost layer of energy dissipating material, e.g.,in contact with the PV, may include a sensor configured to detecteventual leaks. However, it will be appreciated that the container'sabsorption of any impact damage, rather than by the pressure vessel, mayresult in relatively little down time of the storage/fuel cell unitfollowing such an impact.

In some examples, at least part of the inner shell of the container,closer to the pressure vessel, could be made of helicoidally arrangedUHMWPE, para-aramid fibers, or other fibers disclosed herein. Suchhelicoidally arranged materials may be expected to provide a relativelylarge reduction in back face deflection during ballistic andhigh-velocity impacts, leading to smaller blunt during the impact event.This is expected to further reduce the likelihood of an impact piercingthrough the container and transferring the momentum to a localizedregion in the PV, further improving impact tolerance.

It should further be noted that helicoidal fiber arrangement mayfacilitate dissipation of energy from an impact through the formation ofmatrix damage, including spiraling matrix splits and delamination. Someexamples herein may include embedded thermoplastic strips of fiberreinforced material or thermoplastic veils which may be used to “heal”such matrix damage. For example, heat and/or pressure may be applied tothe damaged container, causing the thermoplastic material to melt andre-fill the cracked matrix. This may significantly extend the usablelifetime of the container.

Additionally, as described in greater detail above, the presentcontainers may include two or more parts so as to readily accommodatethe insertion of a PV. As such, the containers may readily be replacedif damaged (and optionally healed in a manner such as described above).Illustratively, two identical half shells may be assembled and connectedaround a sagittal plane defined by the PV shape, e.g., in a manner suchas described with reference to FIG. 2A. Alternatively, the hollow shellsmay be formed to define an axisymmetric over vessel shape with a domeopening to slide the HPV inside, e.g., in a manner such as describedwith reference to FIG. 2B. In some examples, the container may beinstalled following pressurization as to inhibit a changing stress orload on the container that otherwise may reduce impact resistance.

While some examples of operations for preparing the present containersare described with reference to FIGS. 9-12 , it will be appreciated thatthe present containers may be prepared using any suitable combination oftechniques, including but not limited to resin transfer molding,infusion, compression press molding, fiber winding, and automated fiberplacement. In a manner such as described with reference to FIG. 10 , thefibers may be placed directly onto the energy dissipating material.Alternatively, in a manner such as described with reference to FIG. 11 ,the fibers may be placed onto a mandrel/male mold to form a shell, andthe energy dissipating material (e.g., foam, such as expandable PU) maybe injected inside the shell; a smaller male mandrel may be used toleave a radial space defining the foam liner thickness. In still otherexamples, preparing the container may include filament windinghelicoidally fibrous layers over a closed cell foam axisymmetric mandrelto constitute the core of the structure, or over an axisymmetric mandrelto secure a high compaction of the plies and the energy dissipatingmaterial may be inserted after the fabrication of a shell. Additionally,or alternatively, the energy dissipating material may be 3D printed ormilled or stamped. Additionally, or alternatively, the energydissipating material may include or consist of filament wound flexiblefoam, which itself may be helically or helicoidally wound.

As will be apparent from examples such as described with reference toFIGS. 1A-1B and 2B, the use of an at least partially cylindrical centralpart with one or two openings may allow for sliding of the PV in and outfrom both sides. In some examples, caps may be configured to allowaccess to the inlet (neck) of the vessel and may at least partiallycover connection pipe(s). A threaded end cap, e.g., such as describedwith reference to FIG. 2B, is one example of a manner in which a cap maybe attached to an at least partially cylindrical central part.

FIG. 15A-15C schematically illustrate various views of another exemplarycontainer 1501 for PV 100. As described above, container 1501 mayinclude any suitable combination of shapes suitable to at leastpartially enclose PV 100. Container 1501 may include one or more hollowshell assemblies formed of one or more hollow shells, and shaped so asto follow the form of, and contact, the respective portions of the outersurface of PV 100. As shown in FIG. 15B, container 1501 may includefirst hollow shell assembly 1510 sized and shaped to at least partiallyenclose a first portion of PV 100, and second hollow shell assembly 1520sized and shaped to enclose a second portion of PV 100, e.g., a portionof PV 100 opposite to the first portion of PV 100 enclosed by firsthollow shell assembly 1510. As such, different portions of the hollowshell assemblies 1510, 1520 may be shaped differently than one another,and may have any suitable cross-section. Illustratively, at least one ofthe inner surfaces of hollow shell assemblies 1510, 1520 is at leastpartially cylindrical, at least partially spherical, or at leastpartially conical. For example, first hollow shell assembly 1510 may beconsidered to define a first bowl shape, and second hollow shellassembly 1520 may be considered to define a second bowl shape.

As shown in FIG. 15A, first hollow shell assembly 1510 may include firsthollow shell 1502 and second hollow shell 1504 attached to first hollowshell 1502. First hollow shell 1502 may have an first inner surface thatis sized and shaped to cover at least a portion of PV 100, and secondhollow shell 1504 may have a second inner surface that is sized andshaped to at least partially cover the outer surface of first hollowshell 1502 so as to define a volume for at least partially enclosing PV100. First and/or second hollow shells 1502, 1504 may include one ormore plies, each of which may have any suitable configuration asdescribed above. For example, the composition and material structure offirst hollow shell 1502 may be similar to, or may be different than,that of second hollow shell 1504. In some examples, first hollow shell1502, second hollow shell 1504, or both, may include a woven fabric, abraided layer, or one or more helical plies. As described above, firstand second hollow shells 1502, 1504 may include a combination of energydissipating materials that are substantially concentric with therespective inner surfaces, and at least partially impregnated with aresin. First and second hollow shells 1502, 1504 are preferably attachedto one another. For example, second hollow shell 1504 may be attached onfirst hollow shell 1502 to partially or fully encase first hollow shell1502 as shown in FIG. 15A. First and second hollow shells 1502, 1504 mayform a multiaxial fabric placed on top of the pressure vessel. First andsecond hollow shells 1502 may be two or more layers of multiaxialfabrics made of helicoidally ranged plies laid up one on top of eachother. In some examples, the helicoidally arranged plies may be in theform of multiaxial non-crimp fabrics. In some other examples, thehelicoidally arranged plies may be in the form of continuous ordiscontinuous fiber tapes helicoidally ranged to one another. Thefabrics may be held together by the same resin that impregnates all theother plies within each fabric. In some embodiments, each hollow shellis made from a plurality of individual plies. For example, Helicoidfabrics made of 10 individual plies could be formed from a first hollowshell having 5 plies and a second hollow shell having the remaining 5plies.

As shown in FIG. 15B, first and second hollow shell assemblies 1510,1520 may be disposed on opposite sides of PV 100, such that the middleportion of PV 100 is unenclosed. Moreover, first hollow shell assembly1510 may be sized and shaped such that at least a portion of the firstportion of PV 100 remains unenclosed, e.g., the rounded portion of PV100. Similarly, second hollow shell assembly 1520 may be sized andshaped such that at least a portion of the second portion of PV 100remains unenclosed, e.g., neck portion 101 of PV 100.

As shown in FIG. 15C, each of first and second hollow shell assemblies1510, 1520 may be formed of one or more fiber layers. The first and/orsecond fiber layers of first and second hollow shell assemblies 1510,1520 may include helical layers (e.g., a plurality of plies) wound in ahelicoidal layup as described above. For example, both first and secondhollow shells 1502, 1504 may include helical layers. Alternatively,first hollow shell 1502 may include helical layers while second hollowshell 1504 does not, or second hollow shell 1504 may include helicallayers while first hollow shell 1502 does not.

Referring now to FIG. 16 , method 1600 for making container 1501 for PV100 is provided. Method 1600 may include winding layers, e.g., helicallayers, to form the shape of PV 100 (operation 1610), e.g., using amandrel. For example, first and second hollow shell assemblies 1510,1520 may be formed to at least partially enclose PV 100. First andsecond hollow shell assemblies 1510, 1520 may include a multi-axialhelicoidal fabric, e.g., a stack-up of quadriaxial, triaxial, or biaxiallayers, or any combination thereof. For example, FIG. 17 illustrates ahelicoidal fabric having quadriaxial layers 1702, 1704, 1706, 1708. Asshown in FIG. 17 , each of layers 1702, 1704, 1706, 1708 may include adifferent orientation. As shown in FIG. 18 , first and second hollowshell assemblies 1510, 1520 may be formed via a tailored, automatedfiber placement blanket. For example, the helicoidal layup sequence maybe created via automated tape manufacturing. Accordingly, the placementof patches of materials may follow a helicoidal layup sequence.

The patches include a single fiber type, or a mixture of fiber typesincluding, for example, glass, carbon, nature fiber, aramid, etc.Moreover, the patches may be formed of dry reinforcement and impregnatedduring placement thereof. Alternatively, the patches may be formed of acompatible pre-impregnated material prior to placement thereof. In someembodiments, the patches may include a thermoplastic and may be appliedas an after-market solution to PV 100.

Referring again to FIG. 16 , method 1600 further may includeoverwrapping the helicoidally wound plurality of plies of first andsecond hollow shell assemblies 1510, 1520 (operation 1620), e.g., viafilament winding, as shown in FIG. 19 , which at least partially enclosePV 100 and which may be at least partially impregnated as describedabove. FIG. 19 illustrates container 1501 partially overwrapped viafilament winding to form layer 2002.

As shown in FIG. 20 , the outer layer of container 1501 may be fullyoverwrapped, such that layer 2002 fully extends on the outer surface ofcontainer 1501 and PV 100. Layer 2002 may follow a helicoidal layupsequence as described above. Alternatively, layer 2002 may not follow ahelicoidal layup sequence. Referring again to FIG. 16 , method 1600further may include co-curing container 1501 (including layer 2002)(operation 1630), and removing the mandrel (operation 1640).

While various illustrative embodiments of the invention are describedabove, it will be apparent to one skilled in the art that variouschanges and modifications can be made therein without departing from theinvention. The appended claims are intended to cover all such changesand modifications that fall within the true spirit and scope of theinvention.

What is claimed:
 1. An apparatus for protecting a pressure vessel, theapparatus comprising: a first hollow shell comprising a first innersurface configured to cover a first portion of the pressure vessel; anda second hollow shell comprising a second inner surface and configuredto be attached to the first hollow shell so as to define a volume for atleast partially enclosing the pressure vessel, wherein the first andsecond hollow shells are configured to be attached to one another so asto overwrap the pressure vessel with a plurality of plies, wherein atleast a portion of the plurality of plies are helicoidally arrangedrelative to one another.
 2. The apparatus of claim 1, wherein the firstand second hollow shells define a volume for fully enclosing thepressure vessel.
 3. The apparatus of claim 1, wherein the first andsecond inner surfaces are at least partially cylindrical, at leastpartially spherical, or at least partially conical.
 4. The apparatus ofclaim 1, wherein the plurality of plies comprise a plurality of helicalplies that are helicoidally arranged relative to one another.
 5. Theapparatus of claim 1, wherein the plies comprise interwoven tows.
 6. Theapparatus of claim 1, further comprising: a third hollow shellcomprising a third inner surface configured to cover a second portion ofthe pressure vessel; and a fourth hollow shell comprising a fourth innersurface and configured to be attached to the third hollow shell so as todefine a volume for at least partially enclosing the pressure vessel. 7.The apparatus of claim 6, wherein the first and second hollow shellsdefine a volume for at least partially enclosing the first portion ofthe pressure vessel, and wherein the third and fourth hollow shellsdefine a volume for at least partially enclosing the second portion ofthe pressure vessel.
 8. The apparatus of claim 7, wherein the firstportion of the pressure vessel is on a side of the pressure vesselopposite to the second portion of the pressure vessel.
 9. The apparatusof claim 1, further comprising a third hollow shell comprising a thirdinner surface and configured to be attached to the second hollow shellso as to define the volume for at least partially enclosing the pressurevessel.
 10. The apparatus of claim 9, further comprising a fourth hollowshell comprising a fourth inner surface and configured to be attached tothe third hollow shell so as to define the volume for at least partiallyenclosing the pressure vessel.
 11. The apparatus of claim 1, wherein thefirst hollow shell comprises a first fiber layer that is substantiallyconcentric with the first inner surface and is at least partiallyimpregnated with a resin.
 12. The apparatus of claim 11, wherein thefirst hollow shell further comprises a first energy dissipating materialthat is substantially concentric with the first inner surface and isdisposed between the first inner surface and the first fiber layer. 13.The apparatus of claim 11, wherein the first fiber layer comprises a dryreinforcement configured to be impregnated during placement of the firsthollow shell on the pressure vessel.
 14. The apparatus of claim 11,wherein the second hollow shell comprises a second fiber layer that issubstantially concentric with the second inner surface and is at leastpartially impregnated with a resin.
 15. The apparatus of claim 14,wherein the second hollow shell further comprises a second energydissipating material that is substantially concentric with the secondinner surface and is disposed between the second inner surface and thesecond fiber layer.
 16. The apparatus of claim 14, wherein the secondfiber layer comprises a dry reinforcement configured to be impregnatedduring placement of the second hollow shell on the first hollow shell.17. The apparatus of claim 1, wherein at least one of the first orsecond hollow shells comprises at least one of glass, carbon, naturalfiber, or aramid.
 18. The apparatus of claim 1, wherein at least one ofthe first or second hollow shells comprises a thermoplastic.
 19. Theapparatus of claim 1, wherein at least one of the first or second hollowshells are formed via automated tape manufacturing.
 20. The apparatus ofclaim 1, further comprising an outer layer comprising a filament windingconfigured to be attached to an outermost layer of the apparatus so asto define a volume for enclosing the pressure vessel.